The following document lists the file abstract/NTRAMS_LMCSICA.abs
from catalogue VI/111.
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The recent discovery of one high luminosity carbon star in the SMC by Whitelock et al (1989) indicates that the formation of C stars at sub solar metallicities may be discouraged but is not excluded as was predicted by stellar evolution theory including hot bottom burning, and observed in optically selected samples of asymptotic giant branch stars. In our extensive programme using ground based observatories and ISO we found one high luminosity carbon star in the LMC. The 3 micron spectrum of this object (IRAS04496-6958, LI-LMC57) shows a strong 3.1 micron absorption, typical for carbon stars, and also the optical spectrum confirms the carbon rich nature. In our ISO project we obtained a 10 micron spectrum of this source using the ISOCAM-CVF. This spectrum shows an emission at 10 micron, indicative of silicates, and thus oxygen rich dust. If this feature is confirmed it would make this object the first and only known carbon star with oxygen rich dust in the LMC and the only one with a known distance. Unfortunately the spectral range covered in our CVF spectrum is not enough to unambiguously identify the feature. Some galactic carbon stars show in their (SWS) spectra absorptions at about 7 and 15 micron. We can at this moment not exclude the possibility that a similar absorption is present in IRAS04496-6958. The identification of the feature is important since it put strong constraints on evolutionary models (requiring either a very rapid and recent evolution from oxygen to carbon rich, or a stationary oxygen rich dust component, possibly in a disk). We therefore propose to reobserve the object with the CAM CVF to extend the wavelength range of the CVF spectrum. Furthermore we propose to obtain a 60 micron photometric measurement using ISOPHOT in mapping mode to be able to better constrain models of the spectral energy distribution of this object. Preliminary modelling indicates that a long wavelength point is essential to properly define the models.